The SIEA Angiosome: Interindividual Variability Predicted Preoperatively

Sir: We would like to congratulate Holm et al. for their recent work improving our understanding of the superficial blood supply of the anterior abdominal wall for superficial inferior epigastric artery (SIEA) flap harvest.1 The major difficulty in using the SIEA flap for free tissue transfer is the substantial variation in vascular anatomy between individuals, and this has been well highlighted by the authors. There are several components of the study that generate valuable discussion; in addition, we would like to offer our own experience in evaluating the SIEA angiosome. The study by Holm et al. presents a unique and valuable tool for the intraoperative evaluation of SIEA perfusion in an individual. In the study, it is assumed that intraoperative fluorescein injection correlates with in vivo flap viability. However, in our opinion, the results of the study do not emphatically prove that the technique is effective, as there was no control group to show that those flaps with “negative” perfusion tests actually did not completely survive. The report of one patient with partial flap necrosis despite having two vascular pedicles and adequate fluorescein perfusion supports this view. A comparative group may well be considered for future research as a means of justifying this technique for all patients intraoperatively. In fact, it is noteworthy that the complication rates in the SIEA flaps performed in this study were similar to those quoted in the literature. Although the current study used an SIEA diameter greater than 1.5 mm as a criterion for selection and requiring the demonstration of adequate flap perfusion, others such as Spiegel et al.2 have only used the criterion of an SIEA diameter greater than 1.5 mm, with equivalent complication rates (4 percent versus 5 percent partial flap necrosis, respectively). This added criterion by Holm et al. required 44 percent of SIEA flaps to be either augmented by a deep inferior epigastric artery (DIEA) perforator pedicle or switched to a DIEA perforator-only flap. Although it is difficult to justify using a flap with marginal perfusion, the results of an SIEA flap alone in those 44 percent of cases may have demonstrated the effectiveness or otherwise of the technique. The definition used by the authors for the SIEA “angiosome” is also worth discussing. The definition used by the authors of the SIEA angiosome is the total area of perfusion within the lower abdominal flap after SIEA injection, on clamping of the DIEA perforators. Although this is certainly the “flap perfusion volume” of the SIEA, this is not the true definition of a vessel’s angiosome. The definition of an angiosome by Taylor et al. is the volume of tissue supplied by a source artery within the structure of adjacent vascular territories, which cannot be assessed after clamping of adjacent source vessels.3–5 Every vessel branches within its territory to connect adjacent territories, and so direct injection into an SIEA will show the area of perfusion by crossing adjacent angiosome territories. Similarly, there are many factors associated with the amount of perfusion that will be demonstrated on contrast injection, such as vasodilatation, anesthetic drugs, temperature, and others. Although the results of these perfusion tests may well be reflective of flap perfusion, the in vivo angiosome of the SIEA is not likely to be represented on the fluorescence studies presented. The original angiosome studies demonstrated individual vascular territories by contrast injection and dye studies in cadaveric specimens, highlighting choke zones between territories.3–5 An additional tool to assess this in vivo, and indeed preoperatively, is the use of computed tomographic angiography. Computed tomographic angiography is able to effectively demonstrate the following: The presence of the SIEA (in either hemiabdominal wall) The diameter of the SIEAs The more likely angiosome territory of the SIEA The branching pattern, and communication with adjacent territories The DIEA and its perforators, as a tool for preselecting preferentially between a DIEA perforator flap and an SIEA flap In our studies of more than 200 computed tomographic angiography scans for imaging of the abdominal wall vasculature, we have found that the SIEA angiosome is highly variable, matching the findings of Holm et al. There is substantial variability both between sides of a single patient and between patients. The use of computed tomographic angiography to demonstrate the angiosome preoperatively can aid in patient selection for an SIEA flap, planning flap design, and decreasing operating times by localizing the hemiabdomen of choice and the vessel itself. As shown in Figure 1, the angiosomes of the SIEA of each side in a single patient are markedly different. The right SIEA shows large medial and lateral branches, which cross the linea semilunaris to encroach on the midline. The left SIEA is devoid of these branches. As such, its angiosome is narrower and more lateral.Fig. 1.: Preoperative computed tomographic angiography, volume-rendered, three-dimensional reconstruction, demonstrating the SIEA of each hemiabdomen and its angiosomal territory (white oval outline). U, umbilicus.In fact, the preoperative assessment of this anatomy with computed tomographic angiography may augment the intraoperative technique of Holm et al. by preselecting those patients for which the intraoperative assessment should be performed. Warren M. Rozen, M.B.B.S., P.G.Dip.Surg.Anat. Daniel Chubb, M.B.B.S.(Hons.), B.Med.Sc. Damien Grinsell, M.B.B.S. Mark W. Ashton, M.B.B.S., M.D. Jack Brockhoff Reconstructive Plastic Surgery Research Unit Department of Anatomy and Cell Biology University of Melbourne Parkville, Victoria, Australia